Electrolyte and electrochemical device

ABSTRACT

An electrolyte and an electrochemical device, which relates to the field of energy storage materials. The electrolyte includes an additive A, an additive B and an additive C, the additive A selected from a group consisting of multi-cyano six-membered N-heterocyclic compounds represented by Formula I-1, Formula I-2 or Formula I-3, and combinations thereof, the additive B is at least one sulfonate compound, and the additive C is at least one halogenated cyclic carbonate compound. The electrochemical device includes the above electrolyte. The electrolyte of the present disclosure can effectively passivate the surface activity of the positive electrode material, inhibit the oxidation of the electrolyte, and effectively reduce gas production of a battery, meanwhile the electrolyte can be also adsorbed catalytically active of the graphite surface to form a more stable SEI film, thereby effectively reducing side reactions

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on International Application No.PCT/CN2017/093306, filed on Jul. 18, 2017, which claims priority toChinese Patent Application No. 201710574732.5, filed on Jul. 14, 2017,the contents of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present disclosure relates to the field of energy storage materials,and particularly, to an electrolyte and an electrochemical device.

BACKGROUND

Lithium-ion batteries are widely used in electric vehicles and consumerelectronic products due to their advantages of high energy density, highoutput power, long cycle life and small environmental pollution. Thecurrent demand on lithium-ion batteries still includes: high voltage,high power, long cycle life, long storage life and excellent safetyperformance.

Most of the current lithium-ion batteries apply an electrolyte system,in which lithium hexafluorophosphate is used as conductive lithium saltand a cyclic carbonate and/or a chain carbonate is used as solvent.However, the above electrolyte system still has many deficiencies. Forexample, the cycle performance and storage performance of the aboveelectrolyte system need to be improved under a condition of high voltageand high temperature.

The present disclosure aims to overcome the said deficiencies.

SUMMARY

In order to solve the above problems, the inventor conducted intensiveresearches and found that using a multi-cyano six-memberedN-heterocyclic compound and a sulfonate compound together as additivesof the electrolyte can effectively inactivate the surface of a positiveelectrode material, inhibit the positive electrode material fromoxidizing the electrolyte, and effectively reduce gas production of thebattery, meanwhile the additives can be adsorbed on catalytically activesites of the graphite surface to form a more stable SEI film, therebysignificantly reducing side reactions. In this way, the cycleperformance at high temperature and high voltage and the storageperformance of the battery can be improved. The present application iscompleted based on the above concept.

One purpose of the present disclosure is to provide an electrolyteincluding an additive A, an additive B and an additive C.

The additive A is selected from a group consisting of multi-cyanosix-membered N-heterocyclic compounds represented by Formula I-1,Formula I-2 and Formula I-3, and combinations thereof:

wherein R₁, R₂, R₃ and R₄ are each independently selected from a groupconsisting of hydrogen, halogen, substituted or unsubstituted C₁-C₁₂alkyl, substituted or unsubstituted C₁-C₁₂ alkoxy, substituted orunsubstituted C₁-C₁₂ amine group, substituted or unsubstituted C₂-C₁₂alkenyl, substituted or unsubstituted C₂-C₁₂ alkynyl, substituted orunsubstituted C₆-C₂₆ aryl, and substituted or unsubstituted C₄-C₁₂heterocyclic group;

the substituent for the above groups, if present, is independentlyselected from a group consisting of halogen, cyano, C₁-C₆ alkyl, C₂-C₆alkenyl, C₁-C₆ alkoxy, and combinations thereof;

x, y and z are each an integer independently selected from 0-8; and

m, n and k are each an integer independently selected from 0-2;preferably, m, n and k are each independently 1 or 2;

wherein the additive B is at least one sulfonate compound; and

the additive C is at least one halogenated cyclic carbonate compound.

Another purpose of the present disclosure is to provide anelectrochemical device including a positive electrode plate, a negativeelectrode plate, a separator positioned between the positive electrodeplate and the negative electrode plate, and an electrolyte according tothe present disclosure.

The technical solutions of the present disclosure at least have thefollowing beneficial effects:

The addition of both the multi-cyano six-membered N-heterocycliccompound and the sulfonate compound as additives of the electrolyteaccording to the present disclosure can effectively passivate surfaceactivity of the positive electrode material, inhibit the positiveelectrode material from oxidizing the electrolyte, and effectivelyreduce gas production of the battery, meanwhile the additives can beadsorbed on catalytically active sites of the graphite surface to form amore stable SEI film, thereby effectively reducing reductivedecomposition of the electrolyte and effectively reducing sidereactions.

The electrochemical device using the electrolyte according to thepresent disclosure has a good cycle performance at high temperature andhigh voltage and a good storage performance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a nuclear magnetic resonance carbon spectrum of Compound A2;

FIG. 2 is a nuclear magnetic resonance carbon spectrum of Compound A8;and

FIG. 3 is a nuclear magnetic resonance carbon spectrum of Compound A13.

DESCRIPTION OF EMBODIMENTS

In order to clarify invention purpose, technical solutions, andadvantages of the present disclosure, the present disclosure will bedescribed in detail below with reference to the embodiments. It shouldbe understood that the embodiments described in the specification merelyaim to explain the present disclosure, rather than limiting the presentdisclosure. Formulations, ratios, etc. mentioned in the embodiments canbe selected depending upon actual conditions and requirements.

The electrolyte and battery according to the present application aredescribed in detail below.

Firstly, according to a first aspect of the present disclosure, anelectrolyte is described as below. The electrolyte according to thepresent disclosure can be a liquid electrolyte or a solid electrolyte.The electrolyte is embodied as the liquid electrolyte to illustrate thepresent disclosure.

The electrolyte according to the first aspect of the present disclosureincludes an organic solvent, an electrolyte salt, and an additive. Theadditive includes an additive A, an additive B and an additive C. Theadditive A is at least one multi-cyano six-membered N-heterocycliccompound, the additive B is at least one sulfonate compound, and theadditive C is at least one halogenated cyclic carbonate compound.

(Additive A)

The additive A is selected from a group consisting of multi-cyanosix-membered N-heterocyclic compounds represented by Formula I-1,Formula I-2 and Formula I-3, and combinations thereof:

in which R₁, R₂, R₃ and R₄ are each independently selected from a groupconsisting of hydrogen, halogen, substituted or unsubstituted C₁-C₁₂alkyl, substituted or unsubstituted C₁-C₁₂ alkoxy, substituted orunsubstituted C₁-C₁₂ amine group, substituted or unsubstituted C₂-C₁₂alkenyl, substituted or unsubstituted C₂-C₁₂ alkynyl, substituted orunsubstituted C₆-C₂₆ aryl, and substituted or unsubstituted C₄-C₁₂heterocyclic group;

the substituent for the above groups, if present, is independentlyselected from a group consisting of halogen, cyano, C₁-C₆ alkyl, C₂-C₆alkenyl, C₁-C₆ alkoxy, and combinations thereof;

x, y and z are each an integer independently selected from 0-8; and

m, n and k are each an integer independently selected from 0-2.

Since the multi-cyano six-membered N-heterocyclic compound have cyanogroups and the nitrogen atoms in the cynao groups can be stronglycomplexed with transition metals, the multi-cyano six-memberedN-heterocyclic compound applied in the electrolyte can be adsorbed onthe surface of the positive electrode material to form a loose porousprotective film. The porous protective film isolates the surface of thepositive electrode material from the electrolyte without affectingnormal transportation of lithium ions, reduces the surface activity ofthe positive electrode material, and meanwhile inhibits a large numberof side reactions occurring on the surface, thereby reducing by-productsand inhibiting gas production.

Further, although the multi-cyano six-membered N-heterocyclic compoundaccording to the present disclosure is a nitrile-derived compound, aspecial six-membered N-heterocyclic structure thereof can affect a filmforming potential of the cynao group and a film forming effect on thesurface of the positive electrode material, and further can improveelectrochemical performance of the entire battery system, such asreducing gas production, increasing cycle life at high temperature andhigh voltage, etc.

(I) In the embodiments of the present application, the compoundsrepresented by Formula I-1 are multi-cyano pyrimidine compounds.

As an improvement of the compounds represented by Formula I-1, R₁, R₂,R₃ and R₄ are each independently selected from a group consisting ofhydrogen, halogen, substituted or unsubstituted C₁-C₆ linear or branchedalkyl, substituted or unsubstituted C₅-C₉ cycloalkyl, substituted orunsubstituted C₁-C₆ alkoxy, substituted or unsubstituted C₁-C₆ aminegroup, substituted or unsubstituted C₂-C₆ alkenyl, substituted orunsubstituted C₂-C₆ alkynyl, substituted or unsubstituted C₆-C₁₂ aryl,and substituted or unsubstituted C₄-C₁₂ heterocyclic group. Thesubstituent for the above groups, if present, is halogen.

As an improvement of the compounds represented by Formula I-1, R₁, R₂,R₃ and R₄ each are independently selected from a group consisting ofhydrogen, halogen, substituted or unsubstituted C₁-C₃ linear or branchedalkyl, substituted or unsubstituted C₅-C₇ cycloalkyl, substituted orunsubstituted C₁-C₃ alkoxy, substituted or unsubstituted C₁-C₃ aminegroup, substituted or unsubstituted C₂-C₃ alkenyl, substituted orunsubstituted C₂-C₃ alkynyl, substituted or unsubstituted C₆-C₈ aryl,and substituted or unsubstituted C₄-C₇ heterocyclic group. Thesubstituent group for the above groups, if present, is halogen.

Each of alkyl, alkenyl and alkynyl can be a chain substituent or acyclic substituent, and the chain substituent can be either a linearsubstituent or a branched substituent.

In the compounds represented by Formula I-1, x is preferably an integerselected from 0-6, further preferably an integer selected from 0-4, morepreferably 1 or 2; and y is preferably an integer selected from 0-6,further preferably an integer selected from 0-4, more preferably 1 or 2.

As an improvement of the compounds represented by Formula I-1, R₁ and R₃are identical; optionally, R₁, R₃ and R₄ are identical.

As an improvement of the compounds represented by Formula I-1, both R₁and R₃ are hydrogen; optionally, R₁, R₃ and R₄ are hydrogen.

As an improvement of the compounds represented by Formula I-1, R₁ to R₄all are hydrogen; or R₁, R₃ and R₄ are hydrogen, R₂ is selected from agroup consisting of halogen, substituted or unsubstituted C₁-C₆ linearor branched alkyl, and substituted or unsubstituted C₁-C₆ alkoxy; andthe substituent for the above groups, if present, is halogen, preferablyfluorine.

As an improvement of the compounds represented by Formula I-1, thecompounds represented by Formula I-1 are selected from, but not limitedto, a group consisting of the following compounds:

(II) In the embodiments of the present disclosure, the compoundsrepresented by Formula I-2 are multi-cyano piperazine compounds.

As an improvement of the compounds represented by Formula I-2, R₁, R₂,R₃ and R₄ each are independently selected from a group consisting ofhydrogen, halogen, substituted or unsubstituted C₁-C₆ linear or branchedalkyl, substituted or unsubstituted C₅-C₉ cycloalkyl, substituted orunsubstituted C₁-C₆ alkoxy, substituted or unsubstituted C₁-C₆ aminegroup, substituted or unsubstituted C₂-C₆ alkenyl, substituted orunsubstituted C₂-C₆ alkynyl, substituted or unsubstituted C₆-C₁₂ aryl,and substituted or unsubstituted C₄-C₁₃ heterocyclic group; and asubstituent for the above groups, if present, is halogen.

As an improvement of the compounds represented by Formula I-2, R₁, R₂,R₃ and R₄ each are independently selected from a group consisting ofhydrogen, halogen, substituted or unsubstituted C₁-C₃ linear or branchedalkyl, substituted or unsubstituted C₅-C₇ cycloalkyl, substituted orunsubstituted C₁-C₃ alkoxy, substituted or unsubstituted C₁-C₃ aminegroup, substituted or unsubstituted C₂-C₃ alkenyl, substituted orunsubstituted C₂-C₃ alkynyl, substituted or unsubstituted C₆-C₈ aryl,and substituted or unsubstituted C₄-C₇ heterocyclic group; and thesubstituent for the above groups, if present, is halogen.

Each of alkyl, alkenyl and alkynyl can be a chain substituent or acyclic substituent, and the chain substituent can be either a linearsubstituent or a branched substituent.

In the compounds represented by Formula I-2, x is preferably an integerselected from 0-6, further preferably an integer selected from 0-4, morepreferably 1 or 2; and y is preferably an integer selected from 0-6,further preferably an integer selected from 0-4, more preferably 1 or 2.

As an improvement of the compounds represented by Formula I-2, at leasttwo of R₁, R₂, R₃ and R₄ are identical; and optionally, at least threeof R₁, R₂, R₃ and R₄ are identical.

As an improvement of the compounds represented by Formula I-2, at leasttwo of R₁, R₂, R₃ and R₄ are hydrogen; and optionally, at least three ofR₁, R₂, R₃ and R₄ are hydrogen.

As an improvement of the compounds represented by Formula I-2, R₁ to R₄all are hydrogen; or at least three of R₁, R₂, R₃ and R₄ are hydrogenand the remaining one of R₁, R₂, R₃ and R₄ is selected from a groupconsisting of halogen, substituted or unsubstituted C₁-C₆ linear orbranched alkyl, and substituted or unsubstituted C₁-C₆ alkoxy; and thesubstituent for the above groups, if present, is halogen, and preferablyfluorine.

As an improvement of the compounds represented by Formula I-2, thecompounds represented by Formula I-2 are selected from, but not limitedto, a group consisting of the following compounds:

cent of the electrolyte in the embodiments of the present disclosure,the additive A is 0.001% to 10% by weight of the electrolyte. If thecontent of the additive A is too low, the improvement effect on theelectrolyte will be not significant. If the content of the additive A istoo high, a complex layer to be formed will have a great thickness,which significantly increases impedances of the positive and negativeelectrodes and thus leads to a deterioration of battery performance.

In the embodiments of the present disclosure, the additive A is at most10%, 9%, 8%, 7%, 6%, 5%, 4.5%, 4%, 3.5%, 3%, 2%, 1.5%, 1.2% or 1.0%, byweight of the electrolyte, and at least 0.001%, 0.005%, 0.01%, 0.05%,0.1%, 0.3%, 0.5%, 0.6%, 0.8%, or 0.9%, by weight of the electrolyte.

Preferably, the additive A is 0.01% to 6%, preferably 0.1% to 3.5% byweight of the electrolyte.

(Additive B)

The sulfonate compound, as the additive B, can be selected from a groupconsisting of a group consisting of a sultone compound, a disulfonatecompound, and combinations thereof. The additive B has a relatively highreduction potential, and thus can be preferentially reduced on thegraphite electrode surface. The reduction product containing sulfurelement is adsorbed on catalytically active sites of the graphitesurface to form a more stable SEI film, thereby effectively reducing thereductive decomposition of the electrolyte and reducing the sidereactions.

Specifically, the sultone compound is at least one of compoundsrepresented by Formula II-1,

in which R₂₁ is selected from substituted or unsubstituted C₁-C₆alkylene, and substituted or unsubstituted C₂-C₆ alkenylene, where thesubstituent for the above groups, if present, is halogen, C₁-C₃ alkyl,or C₂-C₄ alkenyl.

Further optionally, R₂₁ is selected from substituted or unsubstitutedC₁-C₄ alkylene, and substituted or unsubstituted C₂-C₄ alkenylene, wherethe substituent for the above groups, if present, is halogen, C₁-C₃alkyl, or C₂-C₄ alkenyl.

Specifically, the sultone compound is selected from 1,3-propane sultone(abbreviated as PS), 1,3-propene sultone (abbreviated as PES), andcombinations thereof. Structural formulas of PS and PES are shown asfollows:

Specifically, the disulfonate compound is at least one of compoundsrepresented by Formula II-2,

in which R₂₂, R₂₃, R₂₄ and R₂₅ are each independently selected fromhydrogen, halogen, substituted or unsubstituted C₁-C₁₀ alkyl, andsubstituted or unsubstituted C₂-C₁₀ alkenyl, where the substituent forthe above groups, if present, is halogen, C₁-C₃ alkyl, or C₂-C₄ alkenyl.

Further optionally, R₂₂, R₂₃, R₂₄ and R₂₅ are each independentlyselected from hydrogen, halogen, substituted or unsubstituted C₁-C₆alkyl, and substituted or unsubstituted C₂-C₆ alkenyl, where thesubstituent for the above groups, if present, is halogen, C₁-C₃ alkyl,or C₂-C₄ alkenyl.

Methylene disulfonate compound can be methylene methanedisulfonate(abbreviated as MMDS):

The methylene disulfonate compound can also be selected from a groupconsisting of 3-methyl-methylene methanedisulfonate, compounds havingthe following structures, and combinations thereof:

As an improvement of the electrolyte in the embodiments of the presentdisclosure, the additive B is 0.1% to 10% by weight of the electrolyte.If the content of the additive B is too low, the improvement effect onthe electrolyte will be not significant. If the content of the additiveB is too high, the formed SEI film will have a great thickness, whichadversely affects a cycle capacitance retention rate of the battery andthus deteriorates battery performance

In the embodiments of the present disclosure, the additive B is at most10%, 9%, 8%, 7%, 6%, 5%, 4.5%, 4%, 3.5%, 3%, 2%, or 1.8%, by weight ofthe electrolyte, and at least 0.1%, 0.25%, 0.25%, 0.3%, 0.5%, 0.6%,0.8%, 0.9%, 1.0%, 1.2%, or 1.5%, by weight of the electrolyte.

Further, the additive B is 0.5% to 7%, preferably 1% to 4% by weight ofthe electrolyte.

(Additive C)

Other additive, as an additive C, can be further added to theelectrolyte according to the embodiments of the present disclosure.Specifically, the additive C can be selected from halogenated cycliccarbonate compounds. The unsaturated bond in the additive C is conduciveto forming a dense negative electrode SEI film, which prevents a contactbetween the negative electrode and the electrolyte, therebysignificantly reducing side reactions.

Specifically, the halogenated cyclic carbonate compound is selected froma group consisting of compounds represented by Formula III andcombinations thereof:

in which R₃₁ is selected from halogenated C₁-C₆ alkylene, andhalogenated C₂-C₆ alkenylene.

Further optionally, R₃₁ is selected from halogenated C₁-C₄ alkylene, andhalogenated C₂-C₄ alkenylene.

The halogenated cyclic carbonate compound is selected a group consistingof the following compounds and combinations thereof:

As an improvement of the electrolyte of the embodiments of the presentdisclosure, the additive C is 0.1% to 10% by weight of the electrolyte.If the content of additive C is too low, the improvement effect ofadditive C on the electrolyte will be not significant. If the content ofthe additive C is too high, the formed SEI film will be too thick, whichadversely affects the cycle capacitance retention rate of the batteryand negatively affects the performance of the battery.

In the embodiments of the present disclosure, the additive C is at most10%, 9%, 8%, 7%, 6%, 5%, 4.5%, 4%, 3.5%, 3%, 2%, or 1.8%, by weight ofthe electrolyte, and at least 0.1%, 0.2%, 0.25%, 0.3%, 0.5%, 0.6%, 0.8%,0.9%, 1.0%, 1.2%, or 1.5%, by weight of the electrolyte.

Further preferably, the additive C is 0.5% to 6%, more preferably 1% to4% by weight of the electrolyte.

In the Formula I-1, Formula I-2, and Formula I-3 in the embodiments ofthe present disclosure:

C₁-C₁₂ alkyl is alkyl having 1 to 12 carbon atoms, and can be a chainalkyl or a cycloalkyl; hydrogen on a ring of cycloalkyl can besubstituted by alkyl; a preferable lower limit of a number of carbonatoms of alkyl is 1, 2, 3, 4, or 5; and a preferable upper limit of thenumber of carbon atoms of alkyl is 3, 4, 5, 6, 8, 10, or 12. Preferably,alkyl having 1-10 carbon atoms is selected; more preferably, a chainalkyl having 1-6 carbon atoms or a cycloalkyl having 3-8 carbon atoms isselected; and most preferably, a chain alkyl having 1-4 carbon atoms ora cycloalkyl having 5-7 carbon atoms is selected. Examples of alkylinclude: methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl,sec-butyl, tert-butyl, n-amyl, iso-amyl, neo-amyl, hexyl, 2-methyl-amyl,3-methyl-amyl, 1,1,2-trimethylpropyl, 3,3,-dimethylbutyl, heptyl,2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, iso-heptyl, octyl,nonyl, and decyl.

Alkoxy is the above-mentioned alkyl having 1-12 carbon atoms and havingoxygen atom. Preferably, alkoxy having 1-10 carbon atoms is selected;more preferably, alkoxy having 1-6 carbon atom is selected; and mostpreferably, alkoxy having 1-4 carbon atoms is selected. Examples ofalkoxy can include: methoxyl, ethoxy, propyloxy, isopropoxy, butoxy,sec-butoxy, tert-butoxy, pentyloxy, iso-pentyloxy, cyclopentyloxy, andcyclohexyloxy.

C₂-C₁₂ alkenyl is alkenyl having 2-12 carbon atoms, and can be a cyclicalkenyl or a chain alkenyl. The alkenyl preferably contains only onedouble-bond. A preferable lower limit of a number of carbon atoms ofalkenyl is 3, 4, or 5, and a preferable upper limit thereof is 3, 4, 5,6, 8, 10, or 12. Preferably, alkenyl containing 2-10 carbon atoms isselected; more preferably, alkenyl containing 2-6 carbon atoms isselected; and most preferably, alkenyl containing 2-5 carbon atoms isselected. Examples of the alkenyl include: vinyl, allyl, isopropenyl,pentenyl, cyclohexenyl, cycloheptenyl, and cyclooctenyl.

C₁-C₁₂ amine group is amine group having 1-12 carbon atoms, and is

where R′ and R″ are each independently alkyl containing 1-12 carbonatoms.

C₂-C₁₂ alkynyl is alkynyl having 2-12 atoms, and can be a cyclic alkynylor a chain alkynyl. Alkynyl preferably contains only one triple bond. Apreferable lower limit of a number of carbon atoms of alkynyl is 3, 4,or 5, and a preferable upper limit thereof is 3, 4, 5, 6, 8, 10, or 12.Preferably, alkynyl containing 2-10 carbon atoms is selected; morepreferably, alkynyl containing 2-6 carbon atoms; and most preferably,alkynyl containing 2-5 carbon atoms is selected. Examples of the alkenylinclude: acetenyl, propargyl, isopropynyl, pentynyl.

C₆-C₂₆ aryl is aryl having 6-26 carbon atoms, for example, phenyl,phenylalkyl, aryl containing at least one phenyl such as biphenyl, andpolycyclic aryl such as naphthyl, anthryl, and phenanthryl; the biphenyland the polycyclic aryl can be substituted by alkyl or alkenyl.Preferably, aryl having 6-16 carbon atoms is selected; more preferably,aryl containing 6-14 carbon atoms is selected; and most preferably, anaryl containing 6-9 carbon atoms is selected. Examples of the arylinclude: phenyl, benzyl, biphenyl, p-tolyl, o-tolyl, m-tolyl.

C₄-C₁₂ heterocyclic group is a heterocyclic group containing having 4-12carbon atoms, a heteroatom thereof can be oxygen, nitrogen, sulfur,phosphorus, boron, etc.; and a heterocyclic ring thereof can be a heteroalicyclic ring or a hetero aromatic ring, and can be a five-membered orsix-membered heterocyclic ring or a benzoheterocyclic ring. Preferably,a heterocyclic group having 4-10 carbon atoms is selected; and morepreferably, a heterocyclic group having 4-7 carbon atoms is selected.Specific examples include: furyl, thienyl, pyrrolyl, thiazolyl,imidazolyl, pyridyl, pyrazinyl, pyrimidyl, pyridazinyl, indolyl,quinolyl, etc.

Halogen is fluorine, chlorine, or bromine, and fluorine is preferable.

In the Formula II-1, Formula II-2, and Formula III in the embodiments ofthe present disclosure:

C₁-C₆ alkylene is a linear or branched alkylene having 1-6 carbon atoms;a preferable lower limit of a number of carbon atoms of alkylene is 2 or3, and a preferable upper limit thereof is 4, 5, or 6. Preferably,alkylene having 1-4 carbon atoms is selected. Examples of alkyl includemethylene, ethylene, propylidene, iso-propylidene, butylidene,iso-butylidene, sec-butylidene, pentylidene, hexylidene.

C₂-C₆ alkenylene is a linear or branched alkenylene having 2-6 carbonatoms, and preferably contains only one double bond. A preferable lowerlimit of a number of carbon atoms of alkenylene is 3 or 4, and apreferable upper limit thereof is 3, 4, 5, or 6. Preferably, alkenylenecontaining 2-5 carbon atoms is selected. Examples of the alkenyleneinclude: vinylidene, propylidene, isopropylidene, butenylidene, andpentenylidene.

C₁-C₁₀ alkyl is alkyl having 1 to 10 carbon atoms, and can be a chainalkyl or a cycloalkyl. Hydrogen on a ring of cycloalkyl can besubstituted by alkyl. A preferable lower limit of a number of carbonatoms of alkyl having 1 to 10 carbon atoms can be 1, 2, 3, or 4, and apreferable upper limit of the number of carbon atoms thereof is 3, 4, 5,6, or 8. Preferably, alkyl having 1-6 carbon atoms is selected; morepreferably, a chain alkyl having 1-6 carbon atoms or a cycloalkyl having3-8 carbon atoms is selected; and most preferably, a chain alkyl having1-4 carbon atoms or a cycloalkyl having 5-7 carbon atoms is selected.

C₂-C₁₀ alkenyl is alkenyl containing 2-10 carbon atoms, and can be acyclic alkenyl or a chain alkenyl. The alkenyl preferably contains onlyone double-bond. A preferable lower limit of a number of carbon atoms ofalkenyl is 3, 4, or 5, and a preferable upper limit thereof is 3, 4, 5,6, or 8. Preferably, alkenyl containing 2-8 carbon atoms is selected;more preferably, alkenyl containing 2-6 carbon atoms is selected; andmost preferably, alkenyl containing 2-5 carbon atoms is selected.

C₁-C₁₀ alkyl is alkyl having 1 to 10 carbon atoms, and can be a chainalkyl or a cycloalkyl; hydrogen on a ring of the cycloalkyl can besubstituted by alkyl; a preferable lower limit of a number of carbonatoms of alkyl is 1, 2, 3, or 4; and a preferable upper limit of thenumber of carbon atoms of alkyl is 3, 4, 5, 6, or 8. Preferably, alkylhaving 1-8 carbon atoms is selected; more preferably, a chain alkylhaving 1-6 carbon atoms or a cycloalkyl having 3-8 carbon atoms isselected; and most preferably, a chain alkyl having 1-4 carbon atoms ora cycloalkyl having 5-7 carbon atoms is selected.

C₂-C₁₀ alkenyl is alkenyl having 2-10 carbon atoms, and can be a cyclicalkenyl or a chain alkenyl. The alkenyl preferably contains only onedouble-bond. A preferable lower limit of a number of carbon atoms of thealkenyl is 3, 4, or 5, and a preferable upper limit thereof is 3, 4, 5,6, or 8. Preferably, alkenyl containing 2-10 carbon atoms is selected;more preferably, alkenyl containing 2-6 carbon atoms is selected; andmost preferably, alkenyl containing 2-5 carbon atoms is selected.

Halogen is fluorine, chlorine, or bromine, and fluorine is preferable.

(Organic Solvent)

The organic solvent used in the electrolyte of the embodiments of thepresent disclosure can be preferably selected from the group consistingof cyclic carbonate, chain ester, lactone, ether, amide, andcombinations thereof. In order to further improve the cycle performanceat high temperature and high voltage and the storage performance at hightemperature, the electrolyte preferably contains cyclic carbonate andchain carbonate.

The term “chain ester” used herein is a concept including both chaincarbonate and chain carboxylic acid ester.

Examples of the cyclic carbonate include ethylene carbonate (abbreviatedas EC), propylene carbonate (abbreviated as PC), etc.

Examples of the chain ester include: asymmetric chain carbonate, such asethyl methyl carbonate (abbreviated as MEC), methyl propyl carbonate(abbreviated as MPC), methyl isopropyl carbonate (abbreviated as MIPC),methyl butyl carbonate, and ethyl propyl carbonate; symmetrical chaincarbonate, such as dimethyl carbonate (abbreviated as DMC), diethylcarbonate (abbreviated as DEC), dipropyl carbonate, and dibutylcarbonate; and chain carboxylic acid ester, such as neovalerates (methylneovalerate, ethyl neovalerate, propyl pivalate, etc.), methylpropionate, ethyl propionate, methyl acetate, and ethyl acetate.

Other suitable examples of the organic solvent may include: cyclicester, such as tetrahydrofuran, 2-methyl tetrahydrofuran, 1, 4-dioxane,etc.; chain ester, such as 1, 2-dimethoxyethane, 1, 2-diethoxyethane, 1,2-dibutoxyethane, etc.; amide, such as dimethylformamide; sulfone suchas sulfolane; and lactones such as γ-butyrolactone, γ-valerolactone, andα-angelica lactone.

(Salt for Electrolyte)

The following lithium slats are suitable examples of the salt forelectrolyte of the present disclosure.

(Li Salts-Type 1)

Suitable examples are complex salts of “Lewis Acid and LiF”, such asLiPF₆, LiBF₄, LiAsF₆, LiSbF₆, LiPF₄(CF3)₂, LiPF₃(C₂F₅)₃, LiPF₃(CF₃)₃,LiPF₃(iso-C₃F₇)₃, and LiPF₅(iso-C₃F₇). Preferable examples are LiPF₆,LiBF₄, and LiAsF₆. More preferable examples are LiPF₆ and LiBF₄.

(Li Salts-Type 2)

Suitable examples are “lithium imide salts or methylated lithium salts”,such as LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, (CF₂)₂(SO₂)₂NLi(cyclic), (CF₂)₃(SO₂)₂NLi (cyclic), and LiC(SO₂CF₃)₃. Preferableexamples are LiN(SO₂F)₂, LiN(SO₂CF₃)₂, and LiN(SO₂C₂F₅)₂. Morepreferable examples are LiN(SO₂F)₂ and LiN(SO₂CF₃)₂.

(Li Salts-Type 3)

Suitable examples are “lithium salts containing a S(═O)₂O structure”,such as LiSO₃F, LiCF₃SO₃, CH₃SO₄Li, C₂H₅SO₄Li, C₃H₇SO₄Li, lithiumtrifluoro (methanesulfonyloxy) borate (LiTFMSB), and lithium pentafluoro(methanesulfonyloxy) phosphate (LiPFMSP). Preferable examples areLiSO₃F, CH₃SO₄Li, C₂H₅SO₄Li, and LiTFMSB.

(Li Salts-Type 4)

Suitable examples are “lithium salts containing P═O or Cl═O”, such asLiPO₂F₂, Li₂PO₃F, and LiClO₄. Preferable examples are LiPO₂F₂ andLi₂PO₃F.

(Li Slats-Type 5)

Suitable examples are “lithium salts with oxalate ligands as anions”,such as lithium bis [oxalate-O,O′] borate (LiBOB), lithiumdifluoro[oxlate-O,O′] borate, lithium difluorobis[oxlate-O,O′] phosphate(LiPFO), and lithium tetrafluoro[oxalate-O,O′] phosphate. Preferableexamples are LiBOB and LiPFO. One or more of these lithium salts can beused in the electrolyte.

The lithium salt is preferably selected from the group consisting ofLiPF₆, LiPO₂F₂, Li₂PO₃F, LiBF₄, LiSO₃F, lithiumtrifluoro((methanesulfonyloxy) borate (LiTFMSB), LiN(SO₂F)₂,LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, lithium bis [oxalate-O,O′] borate (LiBOB),lithium difluorobis [oxalate-O,O′] phosphate (LiPFO), lithiumtetrafluoro[oxalte-O,O′] phosphate, and combinations thereof; morepreferably, selected from the group consisting of LiPF₆, LiBF₄, LiSO₃F,lithium trifluoro((methanesulfonyloxy) borate (LiTFMSB), LiPO₂F₂,LiN(SO₂CF₃)₂, LiN(SO₂F)₂, lithium bis[oxalate-O,O′] borate (LiBOB),lithium difluorobis[oxalate-O,O′] phosphate (LiPFO), and combinationsthereof; and most preferably, is LiPF₆.

(Preparation of Electrolyte)

The electrolytes according to the embodiments of the present disclosurecan be obtained by a method as described below, for example, mixing theabove organic solvents, then adding an electrolyte salt, the additive A,the additive B and the additive C.

(Synthesis of Multi-Cyano Six-Membered N-Heterocyclic Compounds)

(I) Preparation of Compounds Represented by Formula I-1:

A reaction equation of the synthesis of compounds represented by FormulaI-1 is shown as below:

Specific steps of the preparation are as follow:

1. An aqueous solution of P-2 (concentration of 30-40%) was addeddropwise to a raw material P-1 within 20-60 min while being stirredrapidly. After the dropwise addition was completed, the mixture wasstirred rapidly for 15-30 h, and then refluxed and stirred for 3-5 hunder temperature of 70-90° C. of oil bath. A colorless, fuming, andviscous liquid intermediate I-1-1 was obtained.

2. K₂CO₃, KI, and anhydrous acetonitrile were added subsequently, andstirred rapidly to form a solid-liquid mixture phase. A raw material P-3was added quickly at 40-60° C., the mixture was further stirred for10-20 h and then cooled to room temperature. A compound represented byFormula I-1 was obtained after separation and purification.

(II) Preparation of Compounds Represented by Formula I-2:

A reaction equation of the synthesis of compounds represented by FormulaI-2 is shown as below:

Specific steps of the preparation are as follow:

Anhydrous sodium carbonate, a raw material P-4 and a raw material P-3were mixed in absolute ethanol, and were stirred to react for 2-5 h. Thereaction mixture was washed for several times with hot ethanol to obtaina crude product, which was recrystallized to obtain a compoundrepresented by Formula I-2.

(III) Preparation of Compounds Represented by Formula I-3:

A reaction equation of the synthesis of compounds represented by FormulaI-3 is shown as below:

Specific steps of the preparation are as follow:

Anhydrous sodium carbonate, a raw material P-5 and a raw material P-3were mixed in absolute ethanol and stirred to react for 2-5 h. Thereaction mixture was washed for several times with hot ethanol to obtaina crude product, which was recrystallized to obtain a compoundrepresented by Formula I-3.

Synthesis Example 1

1. Aqueous solution of formaldehyde (37%) was added dropwise to1,3-propanediamine within 0.5 h and stirred rapidly. After the dropwiseaddition was completed, the mixture was further stirred rapidly for 20h, and refluxed and stirred at a temperature of 80° C. of oil bath for 4h. A colorless, fuming and viscous liquid intermediate,hexahydropyrimidine, was obtained.

2. K₂CO₃, KI, and anhydrous acetonitrile were added subsequently. Themixture was stirred rapidly to form a solid-liquid mixture phase.β-chloropropionitrile was added within 0.5 h at a temperature of 60° C.,then the reaction mixture was cooled to room temperature after beingstirred for 17 h. A Compound A2 was obtained after separation andpurification.

¹³C-NMR of the Compound A2 is shown in FIG. 1.

Synthesis Example 2

Anhydrous sodium carbonate, piperazine and β-chloropropionitrile weremixed in absolute ethanol, and stirred to react for 4 h. The reactionmixture was rinsed for several times with hot ethanol to obtain a crudeproduct, which was recrystallized to obtain a Compound A8.

¹³C-NMR of the Compound A8 is shown in FIG. 2.

Synthesis Example 3

Anhydrous sodium carbonate, 1,3,5-s-triazine and chloroacetonitrile weremixed in absolute ethanol, and stirred to react for 4 h. The reactionmixture was rinsed for several times with hot ethanol to obtain a crudeproduct, which was recrystallized to obtain a Compound A13.

¹³C-NMR of the Compound A13 is shown in FIG. 3.

According to a second aspect of the present disclosure, a battery isdescribed below.

The electrochemical device according to the embodiments of the presentdisclosure includes a positive electrode plate, a negative electrodeplate, a separator disposed between the positive electrode plate and thenegative electrode plate, and an electrolyte. It should be noted thatthe battery according to the embodiments of the present disclosure canbe a lithium-ion secondary battery, a lithium primary battery or alithium-ion capacitor.

When the electrochemical device is a lithium-ion secondary battery, thepositive electrode plate thereof includes a positive electrode activematerial capable of de-intercalating and intercalating lithium ions, andthe negative electrode plate thereof includes a negative electrodeactive material capable of intercalating and de-intercalating lithiumions.

Specifically, when the electrochemical device is a lithium-ion secondarybattery, the positive electrode active material can be selected from thegroup consisting of lithium cobalt oxide, lithium nickel oxide, lithiummanganese oxide, lithium nickel manganese oxide, lithium nickel cobaltmanganese oxide, lithium nickel cobalt aluminum oxide, a compound formedby doping a transition metal or a non-transition metal into the lithiumtransition metal oxides, and combinations thereof. The positiveelectrode active material can be a layered lithium-containing oxide, aspinel-type lithium-containing oxide, an olivine-type lithium-containingphosphate compound or the like. However, the positive electrode activematerial is not limited to the above materials. Any conventionalmaterial that can be used as a positive electrode active material of alithium-ion battery can be adopted. These positive electrode activematerials can be used individually or in combination. The negativeelectrode active material can be soft carbon, hard carbon, artificialgraphite, natural graphite, silicon, silicon oxide, silicon carboncomposite, lithium titanate, metal capable of forming an alloy withlithium, or the like. Specifically, a carbon-based negative electrode, asilicon-based negative electrode, a tin-based negative electrode, or thelike can be used. However, the negative electrode active material is notlimited to these materials. Any conventional material that can be usedas a negative electrode active material of a lithium-ion battery can beadopted. These negative electrode active materials can be usedindividually or in combination.

Specifically, when the electrochemical device is a lithium primarybattery, the negative electrode material of the lithium primary batteryis lithium metal or lithium alloy; the the common positive electrodeactive materials of the lithium primary battery include: solid halidesuch as copper fluoride (CuF₂), copper chloride (CuCl₂), silver chloride(AgCl), polyfluorocarbon ((CF)₄), solid sulfide such as copper sulfide(CuS), iron sulfide (FeS), iron disulfide (FeS₂), solid oxide such asmanganese dioxide (MnO₂), copper oxide (CuO), molybdenum trioxide(MoO₃), vanadium pentoxide (V₂O₅), solid oxyacid salts such as silverchromate (Ag₂CrO₄) and lead citrate (Pb₂Bi₂O₅).

When the electrochemical device is a lithium-ion capacitor, the negativeelectrode material of the lithium-ion capacitor is graphite or apolyacene material, and the positive electrode material thereof isactivated carbon.

In the above-mentioned electrochemical device, the separator is notspecifically limited, and can be any separator material used in theexisting batteries, such as polyethylene, polypropylene, polyvinylidenefluoride, and a multilayered composite film thereof, but is not limitedthereto.

The electrolyte is the electrolyte according to the first aspect of thepresent disclosure.

In the above-mentioned electrochemical device, the positive electrodeplate further includes a binder and a conductive agent. A positiveelectrode slurry containing the positive electrode active material, thebinder and the conductive agent is coated on a positive currentcollector and then dried to obtain the positive electrode plate.Similarly, a negative electrode slurry containing the negative electrodeactive material, a binder and a conductive agent is coated on a negativecurrent collector, and then dried to obtain the negative electrodeplate.

Further, when the electrochemical device is a lithium-ion secondarybattery, a charging cutoff voltage of the electrochemical deviceaccording to the embodiments of the present disclosure is not less than4.2V. That is, the battery can operate in a range of 4.2V to 4.9V, andfurther optionally in a range of 4.3V to 4.8V. In a high voltage state,the higher the valence state of the surface transition metal of thepositive electrode material, the stronger the coulomb interaction of thecynao groups in the additive, i.e., the stronger the protective effectthe additive can provide.

EXAMPLES

The following specific examples of the present disclosure merelyillustrate the embodiments of the lithium-ion secondary battery (alsoreferred as to lithium-ion battery hereinafter), but the presentdisclosure is not limited thereto. The present disclosure is describedin detail in combination with the examples of the lithium-ion secondarybattery. It should be understood that these examples are merely used toillustrate the present disclosure, but not intended to limit the scopeof the present disclosure. The reagents, materials and instruments usedin the following examples and comparative examples are commerciallyavailable, unless otherwise specified.

Preparation of Electrolyte: A mixture of ethylene carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) was used as solvent,in which a mass ratio of EC, EMC and DEC is 1:1:1. LiPF₆ was used as thelithium salt, and a total content of LiPF₆ is 12.5% of a total weight ofthe electrolyte. The additive is added to the composition of theelectrolyte shown in Table 1 is added, in which the concentrations ofthe additive are ratios of the weight of the additive to the totalweight of the electrolyte.

The used additives are shown as below:

Additive A:

Additive B:

Additive C:

Preparation of Positive Electrode Plate: LiCoO₂ used as the positiveelectrode active material, PVDF used as the binder, and acetylene blackused as the conductive agent were mixed in a mass ratio of 98:1:1, andthen N-methylpyrrolidone was added. The mixture was stirred with avacuum mixer until a stable and uniform positive electrode slurry wasobtained. The positive electrode slurry was uniformly coated on analuminum foil. The aluminum foil was dried in the air at roomtemperature, transferred to a blast oven and dried there at 120° C. for1 h, following by cold pressing and cutting, so as to obtain a positiveelectrode plate.

Preparation of Negative Electrode Plate: Graphite used as the negativeelectrode active material, acetylene black used as the conductive agent,carboxymethyl cellulose sodium (CMC) solution used as a thickener, andstyrene-butadiene rubber emulsion used as the binder were mixed in amass ratio of 97:1:1:1, and then deionized water was then added. Themixture was stirred with a vacuum mixer until a stable and uniformnegative electrode slurry was obtained. The negative electrode slurrywas uniformly coated on a copper foil. The copper foil was dried in theair at room temperature, transferred to a blast oven and dried there at120° C. for 1 h, following by cold pressing and cutting, so as to obtaina negative electrode plate.

Preparation of Battery: The positive electrode plate, the negativeelectrode plate and a PP/PE/PP separator were wound to obtain a cell.After the cell had been placed in a package shell, the electrolyte wasinjected, and the package shell was sealed. Through subsequentprocedures such as storing, hot and cold pressing, formation, airexhausting, capacitance test, a lithium-ion battery was obtained.

In Table 1, the concentrations of the additive A, the additive B and theadditive C are in percentages by weight based on a total weight of theelectrolyte.

TABLE 1 Components and proportion of components in the electrolytes ofBatteries 1-28 and Comparative Batteries Additive A Additive B AdditiveC No. solvent type conc. type conc. type conc. Battery 1 EC:EMC:DEC =1:1:1 A1 0.001%  B1 3.0% C1 2.0% Battery 2 EC:EMC:DEC = 1:1:1 A1 0.01% B1 3.0% C1 2.0% Battery 3 EC:EMC:DEC = 1:1:1 A1 0.1% B1 3.0% C1 2.0%Battery 4 EC:EMC:DEC = 1:1:1 A1 1.0% B1 3.0% C1 2.0% Battery 5EC:EMC:DEC = 1:1:1 A1 2.0% B1 3.0% C1 2.0% Battery 6 EC:EMC:DEC = 1:1:1A1 3.5% B1 3.0% C1 2.0% Battery 7 EC:EMC:DEC = 1:1:1 A1 6.0% B1 3.0% C12.0% Battery 8 EC:EMC:DEC = 1:1:1 A1 8.0% B1 3.0% C1 2.0% Battery 9EC:EMC:DEC = 1:1:1 A1 10.0%  B1 3.0% C1 2.0% Battery 10 EC:EMC:DEC =1:1:1 A1 2.0% B1 0.1% C1 2.0% Battery 11 EC:EMC:DEC = 1:1:1 A1 2.0% B10.5% C1 2.0% Battery 12 EC:EMC:DEC = 1:1:1 A1 2.0% B1 1.0% C1 2.0%Battery 13 EC:EMC:DEC = 1:1:1 A1 2.0% B1 2.0% C1 2.0% Battery 14EC:EMC:DEC = 1:1:1 A1 2.0% B2 3.0% C1 2.0% Battery 15 EC:EMC:DEC = 1:1:1A1 2.0% B3 3.0% C1 2.0% Battery 16 EC:EMC:DEC = 1:1:1 A1 2.0% B1 6.0% C12.0% Battery 17 EC:EMC:DEC = 1:1:1 A1 2.0% B1 10.0%  C1 2.0% Battery 18EC:EMC:DEC = 1:1:1 A1 2.0% B1 3.0% C1 0.1% Battery 19 EC:EMC:DEC = 1:1:1A1 2.0% B1 3.0% C1 1.0% Battery 20 EC:EMC:DEC = 1:1:1 A1 2.0% B1 3.0% C13.0% Battery 21 EC:EMC:DEC = 1:1:1 A1 2.0% B1 3.0% C1 6.0% Battery 22EC:EMC:DEC = 1:1:1 A1 2.0% B1 3.0% C1 10.0%  Battery 23 EC:EMC:DEC =1:1:1 A1 2.0% B1 3.0% C2 2.0% Battery 24 EC:EMC:DEC = 1:1:1 A1 2.0% B23.0% C2 2.0% Battery 25 EC:EMC:DEC = 1:1:1 A1 2.0% B3 3.0% C2 2.0%Battery 26 EC:EMC:DEC = 1:1:1 A1 2.0% B1 3.0% C3 2.0% Battery 27EC:EMC:DEC = 1:1:1 A1 2.0% B2 3.0% C3 2.0% Battery 28 EC:EMC:DEC = 1:1:1A1 2.0% B3 3.0% C3 2.0% Comparative EC:EMC:DEC = 1:1:1 / / / / / /Battery 1 Comparative EC:EMC:DEC = 1:1:1 A1   2% / / / / Battery 2Comparative EC:EMC:DEC = 1:1:1 A1   2% B3 3.0% / / Battery 3 ComparativeEC:EMC:DEC = 1:1:1 A1   2% / / C1 2.0% Battery 24 In Table 1, “/” meansthe additive is absent.

The high-voltage and high-temperature cycle performance of thelithium-ion batteries was evaluated by means of the cycle capacitanceretention rate, and the high-temperature storage performance wasevaluated by means of the thickness expansion ratio of the lithium-ionbatteries. The Batteries 1-28 were tested as follows:

(1) Cycle Performance Test of Lithium-Ion Batteries at High Voltage

At 25° C., the lithium-ion secondary battery was firstly charged with aconstant current of 1 C to a voltage of 4.35 V, further charged at aconstant voltage of 4.35 V until the current was 0.05 C, and thendischarged at a constant current of 1 C to a voltage of 3.0 V. Thisprocedure is called as one charge and discharge cycle, and a dischargecapacitance during this first cycle was referred to as a dischargecapacitance of the 1^(st) cycle. The lithium-ion battery was subjectedto 200 charge and discharge cycles according to the above procedure, andthe discharge capacitance of the 200^(th) cycle was measured.Capacitance retention rate (%) of the lithium-ion battery after 200cycles=(discharge capacitance of the lithium-ion battery in the 200^(th)cycle/discharge capacity of the lithium-ion battery in the 1^(st)cycle)×100%.

(2) Cycle Performance Test of Lithium-Ion Batteries at High Temperatureand High Voltage

At 45° C., the lithium-ion battery was firstly charged with a constantcurrent of 1 C to a voltage of 4.35 V, further charged at a constantvoltage of 4.35 V until the current was 0.05 C, and then discharged at aconstant current of 1 C to a voltage of 3.0 V. This procedure was calledas one charge and discharge cycle, and a discharge capacitance duringthis first cycle was referred to as a discharge capacitance of the1^(st) cycle. The lithium-ion battery was subjected to 200 charge anddischarge cycles according to the above procedure, and the dischargecapacitance of the 200^(th) cycle was measured.Capacitance retention rate (%) of the lithium-ion battery after 200cycles=(discharge capacitance of the lithium-ion battery in the 200^(th)cycle/discharge capacity of the lithium-ion battery in the 1^(st)cycle)×100%.

(3) Storage Performance Test of Lithium-Ion Batteries at HighTemperature

At 85° C., the lithium-ion battery was charged with a constant currentof 0.5 C to a voltage of 4.35 V, and then charged at a constant voltageof 4.35 V until the current was 0.05 C; at this time, the thickness ofthe lithium-ion battery was measured and recorded as h0. The lithium-ionbattery was then placed in an incubator at 85° C., stored for 24 hoursand then taken out; at this time, the thickness of the lithium-ionbattery was measured and recorded as h1.Thickness expansion ratio of the lithium-ion battery after 24h storage(%)=[(h1−h0)/h0]×100%.

TABLE 2 Test results of cycle capacitance retention rate and thicknessexpansion ratio 25° C./4.35 V/ 45° C./4.35 V/ thickness capacitancecapacitance expansion retention rate retention ratio after 24 h No.after 200 cycles rate after 200 cycles storage at 85° C. Battery 1 89%86% 13% Battery 2 91% 88% 10% Battery 3 93% 90% 8% Battery 4 95% 94% 4%Battery 5 99% 98% 2% Battery 6 98% 96% 2% Battery 7 95% 94% 2% Battery 893% 90% 2% Battery 9 90% 86% 1% Battery 10 96% 93% 6% Battery 11 97% 94%5% Battery 12 98% 96% 4% Battery 13 99% 96% 3% Battery 14 99% 98% 2%Battery 15 99% 98% 2% Battery 16 96% 95% 2% Battery 17 94% 91% 1%Battery 18 98% 96% 3% Battery 19 99% 98% 2% Battery 20 96% 96% 2%Battery 21 91% 89% 1% Battery 22 86% 84% 2% Battery 23 98% 96% 3%Battery 24 98% 97% 2% Battery 25 97% 96% 2% Battery 26 98% 96% 3%Battery 27 97% 96% 3% Battery 28 97% 95% 2% Comparative 83% 75% 67%Battery 1 Comparative 94% 91% 7% Battery 2 Comparative 98% 96% 5%Battery 3 Comparative 97% 95% 6% Battery 4

Comparing Batteries 1-28 with Comparative Battery 1, it can be seen thatthe combination of additives added in the electrolyte of the lithium-ionbatteries can significantly improve the cycle performance at highvoltage and high temperature, and the storage performance at hightemperature of the lithium-ion batteries.

It can be seen from Batteries 1-9 that when the charge cut-off voltageis 4.35V, the cycle capacitance retention rates of the battery at 25° C.and 45° C. reached an optimal value and then had a dropping trend, whilebattery expansion rate after 24 h storage at 85° C. kept decreasing,with the increase of the amount of the additive A (0.001% to 10%).

The reason lies in that the multi-cyano six-membered N-heterocycliccompound molecule in the additive A contains two or more cynao groups atthe same time, the nitrogen atoms in these cynao groups contain lonepair electrons, which can be strongly complexed with the 3d empty orbitof the surface transition metal of the positive electrode material. Inthis way, the surface activity of the positive electrode plate isreduced, while the surface of the positive electrode plate (especiallyat high SOC) is prevented from directly contacting the electrolyte.Therefore, side reaction at the surface of the positive electrode plateis significantly reduced, and thus less lithium ions are consumed in theside reaction, i.e., the consumption rate of the reversible lithium ionsis greatly reduced, which results in a significantly enhanced cyclecapacitance retention rate. In addition, since part of the sidereactions on surface can generate gas, the reduction of surface sidereactions means a decrease in gas production, and thus the thicknessexpansion effect of the battery at high temperature is significantlyalleviated.

The cynao group in the additive A can be complexed with both Li⁺ and thetransition metals on the surface of the positive electrode material.Therefore, when the addition amount of the additive A is excessivelygreat, on the one hand, the excessive additive A (except that adsorbedon the surface of the LCO) would consume Li⁺, resulting in a decrease inthe circulating Li⁺ in the battery cell, and on the other hand, it wouldlead to an increase in the overall viscosity of the electrolyte and adecrease in the ionic conductivity, thereby reducing the cyclecapacitance retention rate of the battery cell. When the addition amountof the additive A is too small, the effect would be not significant.

By comparing with Comparative Battery 2, Comparative Battery 3 andComparative Battery 4, it can be seen that addition of the additive A,the additive B and the additive C can effectively reduce the expansionratio of the battery after storage at 85° C., and effectively improvethe cycle performance at 25° C. and 45° C.

The additive B can further improve the cycle performance at hightemperature and high voltage and the storage performance at hightemperature of the lithium-ion battery, and further reduce the gasproduction. The reason lies in that, the additive A can stabilize thepositive electrode surface and reduce the side reactions on the positiveelectrode surface, while the additive B can be preferentially reduced onthe graphite electrode surface due to its relatively high reductionpotential and sulfur element-containing molecules in the reductionproduct are adsorbed on catalytically active sites of the graphitesurface to form a more stable SEI film, so as to effectively reducingthe reductive decomposition of the electrolyte and reducing the sidereactions. Thus, the synergic effect of the additive A and the additiveB further enhances the performance of the lithium-ion battery. The mainmechanism of the effect of the additive C is in that the halogenatedcyclic carbonate is a good film forming additive, which canpreferentially form a film on the anode than other substances in theelectrolyte, thereby preventing damage from the solvent and solvatedlithium ions to the graphite structure. However, if the addition amountis too large, the impedance of the positive electrode will be increased.When the addition amount of the additive C added is small, theimprovement of the performance is not significant, because the amount ofthe additive C participating in the film formation is excessively small,and the additive C can hardly play a significant role. When the additiveC is added too much, the formed SEI film will be too thick, which will,on the one hand, reduce the migration velocity of lithium ions, increasebattery impedance and even lead to lithium precipitation; and on theother hand, excessive film-forming reaction consumes a large number oflithium ions, significantly increasing the irreversible capacitance anddeteriorating the battery performance. When the content of the additiveC is 4%, optimal electrochemical performances such as high/lowtemperature cycle performance, high-temperature storage performance andgas production, were obtained.

In summary, when the addition amounts of the additive A, the additive Band the additive C are 2%, 3% and 2%, respectively, an optimalsynergistic effect was obtained.

OTHER EXAMPLES

Other lithium ion batteries were prepared with the method of the aboveexamples, and the compositions of the electrolytes are shown in Table 3.

In Table 3, the concentrations of the additive A, the additive B and theadditive C are percentage by weight based on the total weight of theelectrolyte.

TABLE 3 Components and proportion of components in the electrolytes ofBatteries 29-45 Additive A Additive B Additive C No. solvent type conc.type conc. type conc. Battery 29 EC:EMC:DEC = 1:1:1 A2 2.0% B1 3.0% C12.0% Battery 30 EC:EMC:DEC = 1:1:1 A3 2.0% B2 3.0% C2 2.0% Battery 31EC:EMC:DEC = 1:1:1 A4 2.0% B3 3.0% C3 2.0% Battery 32 EC:EMC:DEC = 1:1:1AS 2.0% B2 3.0% C2 2.0% Battery 33 EC:EMC:DEC = 1:1:1 A6 2.0% B1 3.0% C12.0% Battery 34 EC:EMC:DEC = 1:1:1 A7 2.0% B2 3.0% C2 2.0% Battery 35EC:EMC:DEC = 1:1:1 A8 2.0% B1 3.0% C1 2.0% Battery 36 EC:EMC:DEC = 1:1:1A9 2.0% B2 3.0% C2 2.0% Battery 37 EC:EMC:DEC = 1:1:1 A10 2.0% B1 3.0%C3 2.0% Battery 38 EC:EMC:DEC = 1:1:1 A11 2.0% B3 3.0% C2 2.0% Battery39 EC:EMC:DEC = 1:1:1 A12 2.0% B1 3.0% C1 2.0% Battery 40 EC:EMC:DEC =1:1:1 A13 2.0% B2 3.0% C3 2.0% Battery 41 EC:EMC:DEC = 1:1:1 A14 2.0% B13.0% C1 2.0% Battery 42 EC:EMC:DEC = 1:1:1 A15 2.0% B3 3.0% C2 2.0%Battery 43 EC:EMC:DEC = 1:1:1 A16 2.0% B1 3.0% C3 2.0% Battery 44EC:EMC:DEC = 1:1:1 A17 2.0% B2 3.0% C2 2.0% Battery 45 EC:EMC:DEC =1:1:1 A18 2.0% B3 3.0% C1 2.0%

The cycle performance at high voltage and high temperature and thestorage performance at high temperature of Batteries 29-45 using theelectrolytes shown in Table 3 are similar to those of Batteries 5, 14and 15, and will not be described in details herein.

According to the disclosure and teachings of the foregoing description,those skilled in the art can also make appropriate changes andmodifications to the embodiments described above. Therefore, the presentdisclosure is not limited to the specific embodiments disclosed anddescribed above, and some modifications and variations shall fall withinthe protection scope of the claims. In addition, although some specificterms used in the specification are merely for convenience ofdescription and do not constitute any limitation.

What is claimed is:
 1. An electrolyte, comprising an additive A, anadditive B and an additive C, wherein the additive A is selected from agroup consisting of multi-cyano six-membered N-heterocyclic compoundsrepresented by Formula I-1, Formula I-3, and combinations thereof:

wherein R₁, R₂, R₃ and R₄ are each independently selected from a groupconsisting of hydrogen, halogen, substituted or unsubstituted C₁-C₁₂alkyl, substituted or unsubstituted C₁-C₁₂ alkoxy, substituted orunsubstituted C₁-C₁₂ amine group, substituted or unsubstituted C₁-C₁₂alkenyl, substituted or unsubstituted C₂-C₁₂ alkynyl, substituted orunsubstituted C₆-C₂₆ aryl, and substituted or unsubstituted C₄-C₁₂heterocyclic group; the substituent for the above groups, if present, isindependently selected from a group consisting of halogen, cyano, C₁-C₆alkyl, C₂-C₆ alkenyl, C₁-C₆ alkoxy, and combinations thereof; x, y and zare each an integer independently selected from 0-8; and m, n and k areeach an integer independently selected from 0-2; preferably, m, n and kare each independently 1 or 2; wherein the additive B is at least onesulfonate compound selected from a group consisting of a sultonecompound, a disulfonate compound, and combinations thereof; and whereinthe additive C is at least one halogenated cyclic carbonate compound,and wherein the additives A and B are independently are from 0.001% to10% by weight of the electrolyte.
 2. The electrolyte according to claim1, wherein R₁, R₂, R₃ and R₄ are each independently selected from agroup consisting of hydrogen, halogen, substituted or unsubstitutedC₁-C₃ linear or branched alkyl, substituted or unsubstituted C₅-C₇cycloalkyl, substituted or unsubstituted C₁-C₃ alkoxy, substituted orunsubstituted C₁-C₃ amine group, substituted or unsubstituted C₂-C₃alkenyl, substituted or unsubstituted C₂-C₃ alkynyl, substituted orunsubstituted C₆-C₈ aryl, and substituted or unsubstituted C₄-C₇heterocyclic group, wherein the substituent for the above groups, ifpresent, is halogen.
 3. The electrolyte according to claim 1, wherein inFormula I-1, R₁ and R₃ are identical, and preferably, R₁, R₃ and R₄ areidentical; and in Formula I-3, at least two of R₁, R₂ and R₃ areidentical.
 4. The electrolyte according to claim 3, wherein in FormulaI-1, R₁ and R₃ are hydrogen; and preferably, R₁, R₃ and R₄ are hydrogen;and in Formula I-3, at least two of R₁, R₂ and R₃ are hydrogen.
 5. Theelectrolyte according to claim 1, wherein the multi-cyano six-memberedN-heterocyclic compound represented by Formula I-1 is selected from agroup consisting of the following compounds and combinations thereof:

the multi-cyano six-membered N-heterocyclic compound represented byFormula I-3 is selected from a group consisting of the followingcompounds and combinations thereof:


6. The electrolyte according to claim 1, wherein the sultone compound isselected from a group consisting of compounds represented by FormulaII-1, and combinations thereof,

wherein R₂₁ is selected from substituted or unsubstituted C₁-C₆alkylene, and substituted or unsubstituted C₂-C₆ alkenylene, wherein thesubstituent for the above groups, if present, is halogen, C₁-C₃ alkyl,or C₂-C₄ alkenyl; and wherein the disulfonate compound is selected froma group consisting of compounds represented by Formula II-2, andcombinations thereof,

wherein R₂₂, R₂₃, R₂₄ and R₂₅ are each independently selected fromhydrogen, halogen, substituted or unsubstituted C₁-C₁₀ alkyl, andsubstituted or unsubstituted C₂-C₁₀ alkenyl, wherein the substituent forthe above groups, if present, is halogen, C₁-C₃ alkyl, or C₂-C₄ alkenyl.7. The electrolyte according to claim 1, wherein the at least onehalogenated cyclic carbonate compound is selected from a groupconsisting of compounds represented by Formula III, and combinationsthereof:

wherein R₃₁ is selected from alkenyl-substituted C₁-C₆ alkylene, andsubstituted or unsubstituted C₂-C₆ alkenylene, wherein the substituentfor the above groups, if present, is selected from a group consisting ofhalogen, C₁-C₆ alkyl, C₂-C₆ alkenyl, and combinations thereof.
 8. Theelectrolyte according to claim 1, wherein the additive C is from 0.1% to10%, by weight of the electrolyte.
 9. An electrochemical device,comprising a positive electrode plate, a negative electrode plate, aseparator positioned between the positive electrode plate and thenegative electrode plate, and an electrolyte according to claim
 1. 10.The electrochemical device according to claim 9, wherein theelectrochemical device is a lithium-ion secondary battery, a lithiumprimary battery, or a lithium-ion capacitor.
 11. The electrochemicaldevice according to claim 9, wherein the electrochemical device is alithium-ion secondary battery, and the lithium-ion secondary battery hasa charge cut-off voltage no less than 4.2V.
 12. The electrolyteaccording to claim 1, wherein the additive A is from 0.01% to 6%, byweight of the electrolyte.
 13. The electrolyte according to claim 1,wherein the additive A is from 0.1% to 3.5%, by weight of theelectrolyte.
 14. The electrolyte according to claim 1, wherein theadditive B is from 0.5% to 7%, by weight of the electrolyte.
 15. Theelectrolyte according to claim 1, wherein the additive B is from 1% to4%, by weight of the electrolyte.
 16. The electrolyte according to claim1, wherein the additive C is from 0.5% to 5%, by weight of theelectrolyte.
 17. The electrolyte according to claim 1, wherein theadditive C is from 1% to 4%, by weight of the electrolyte.